The present invention relates to firearms.
In particular, the present invention relates to firearms such as semiautomatic shotguns utilizing gas under pressure, resulting from firing of a round, in order to operate automatically components of the firearm.
Such firearms have a gas cylinder which receives gas under pressure from the barrel, this gas under pressure acting on a gas piston in the gas cylinder in order to provide the automatic operation. In order to avoid the drawbacks of excessive gas pressure, a relief valve may be provided, and the present invention relates particularly to that part of the firearm which has the relief valve.
Thus, there are known firearms such as semiautomatic shotguns where the gas cylinder-and-piston unit are situated directly on the magazine tube of the gun. For example there are known constructions where the gas cylinder together with the gas piston therein have been mounted to form a continuation of the magazine tube, with the gas piston being movable upon the neck of a separate solid stem member which forms a continuation of the magazine tube. With the design where the gas piston-and-cylinder unit have been placed directly on the magazine tube as well as with the construction where the gas piston-and-cylinder unit forms a continuation of the magazine tube it has been found difficult to accommodate a relief valve for the purpose of equalizing the variations which occur as a result of firing rounds which have charges of various strengths. Thus, the force of the gas under pressure is conventionally utilized to move the gas piston in order to operate a lock which opens a port through which the empty cartridge case is ejected. As a result of charges of various strengths, variations will occur in the force or velocity of the lock return movement, and the purpose of the relief valve is to equalize these variations by automatically reducing the pressure which otherwise would result from a charge of excessive strength.